1. Field of Invention
The invention relates to the production of hydrogen from hydrocarbon fuels, in a manner useful with respect to fuel cells, and more particularly to catalytic cracking of gaseous and distillate hydrocarbon fuels.
2. Description of the Prior Art
The production of hydrogen from hydrocarbon fuels has for the most part involved the use of steam in the well-known steam reform reaction. In the utilization of hydrocarbon fuels for providing hydrogen to a fuel cell, the presence of any water whatsoever in the fuel cell feed can be prohibited due to the environment (freezing temperatures) or due to the lack of a supply of feed water. Therefore, other methods of producing hydrogen have been sought. Most of these employ hydrogen-containing gases other than hydrocarbons, and are therefore limited to utilization where the source of such a gas is readily available. Naturally, this inhibits broad usage of the fuel cell whenever the fuel cell cannot operate on commonly-available fuels such as engine fuels, natural gas and the like.
Attempts have been made in the past to utilize group VIII metals, particularly nickel, to crack hydrocarbon fuels. However, it is believed that such processes have been limited to the cracking of gaseous hydrocarbon fuels, such as natural gas, propane and the like. Furthermore, it has been found that such processes involve an unduly long purge following the burn cycle due to excessive oxidation of the catalysts during the burn cycle (which is interspersed with alternate cracking cycles), particularly when the catalyst of high nickel content is used. On the other hand, use of lower nickel content catalysts has resulted in inefficient processes with a lower yield of hydrogen.
To overcome these problems, an attempt has been made to utilize a low nickel content catalyst at the inlet of the reactor bed and a high nickel content catalyst at the exit. However, such reactors have proved impractical due to spalling of the pellets, nonreduced oxidation of the catalyst, and other problems.